85 Olds Firenza, Locate Tach Wire?

I am trying to setup a remote starter on my beater 85 Olds Firenza.

The ignition coil is pretty old and not readable for the negative side. The wire is supposed to be white and the wires are either red, brown or black.

Stupid question, but using a voltmeter. is there a way to find the negative post of the igntion coil?

thanks

THanks Mike M2

I have found in my manual, supposedly, I can use the white wire coming off the distributer. I am going out right now, to try that wire.

If that doesnt work, I noticed on one of those wires going to the coil, white tape wrapped around the one wire for about 4 inches in length, so I am thinking that might be the white wire on the coil I  am looking.

Xttech

Well, looks like I have found a good tach wire now..off the white wire going to the distributor.

My only problem now, it starts, but the starter stays engaged dragging, then remote control shuts car down.   From the manual, it appears this might be caused by a weak tach signal. or its needs to be tach adjusted again. I tried tach adjustment again and still the same....   I also noted off the distributor there is a PURPLE / white wire and this poss can be a better tach signal as it goes to the engine crankshaft sensor. I am going to try switching this out and see if it is the cause.